The present application is directed to the lighting arts. Typically, high frequency ballast inverter circuits provide power for operating a lamp, and the present application is directed to one of these ballast circuits. More particularly, the present application is directed to a ballast circuit that has the capability to power both a primary and a secondary, backup lamp, and will be described with particular reference thereto.
Typically, in an industrial lighting setting, it is often desirable to have a backup light source available should primary lights fail. Sometimes, in certain settings, it is even required to have automatic backup lighting. Many industrial lighting settings use high intensity discharge (HID) lamps because of their long life, high lumen output, and relative reliability. Yet even the best of light sources will fail from time to time. HID lamps in particular will “drop out” from time to time, meaning that they temporarily stop producing light, but are not dead, or permanently spent.
After lamp drop out, or if power is interrupted to the HID lamp, the lamp cannot be restarted until the lamp cools down. This can take up to twenty minutes, and during that time, the area in which the lamp is fixed will be without light. Temporary lighting is desirable, and often required where failure of primary light sources could present dangerous conditions. Typically, these temporary, backup light sources were powered by their own dedicated drive circuits. It has been typical that these auxiliary drive sources tap the ballasting inductor to provide a 120 V signal to the auxiliary lamp. This means that added space is required in an often already space lacking environment to house the backup drive circuits, and their associated power sources.
When an HID lamp drops out, the voltage inverter of the ballast typically does not simply stop oscillating. The unlit lamp acts essentially as an open circuit as far as the ballast is concerned, but a small amount of current still completes the circuit. Thus the lamp can be re-struck and again ramp up to its steady state operation. In the meantime however, a completely different circuit powers the auxiliary lamp while the primary lamp relights.
The present application presents a new and improved HID ballast inverter circuit that overcomes the above referenced problems and others.